The present invention relates to a pulverized coal firing method and an equipment therefor and, more particularly, to a method of and an equipment for firing pulverized coal carried by combustion air.
Recently, because of a rise in oil fuel prices, a demand for equipment utilizing coal as fuel such as, for example, pulverized coal burning boilers has increased.
In a conventional pulverized coal burning boiler, coal is ground by a mill into pulverized coal, and the pulverized coal is carried by combustion air into a furnace of the boiler and is combusted therewithin. At the early stage of transportation of the pulverized coal, the pulverized coal is no sufficiently formed within the mill and, therefore, an amount of the pulverized coal fed into the furnace, that is, an amount of the pulverized coal with respect to combustion air (a so-called pulverized coal concentration C/A) is low. In addition, at the early stage of operation of the boiler, it is impossible from the viewpoint of safety countermeasure of the boiler to abruptly raise the concentration C/A. Moreover, in order to stably ignite the pulverized coal within the furnace, it is necessary to raise the temperature within the furnace to a level equal to or higher than a given stable ignition temperature (about 500.degree. C.). To this end, in the conventional pulverized coal burning boiler, light oil and/or heavy oil having an ignition temperature lower than that of the coal is combusted at the start-up to burn the pulverized coal of a low concentration and to raise the temperature within the furnace.
In a large-sized boiler, however, several hours are spent in burning the oil at the start-up, so that an excessive amount of oil is consumed.
In view of the above, various measures have been taken to reduce the amount of consumption of the oil at the start-up of the boiler. One of the measures is a so-called bin system disclosed in, for example, JP-U-61-144332, in which pulverized coal is pre-beforehand stored in a pulverized coal storage bin. In the system of this kind, the pulverized coal is fed, at the start-up of the boiler, from the bin into a furnace through a burner device. From the viewpoint of safety countermeasure, however, the bin cannot be arranged in the vicinity of the furnace. In addition, in case of a large-sized boiler for power plant or the like, a line connecting a mill and a burner device is extremely large in diameter. For this reason, it takes a considerable time until pulverized coal and transporting air are sufficiently mixed with each other, and the mixture is sufficiently raised in concentration and is fed into a furnace. Accordingly, the mixture containing the pulverized coal is fed into the furnace without being burned, resulting in an ignition lag. This causes a danger that as combustion is actually initiated, pressure within the furnace rises abnormally, and explosion due to unburnt pulverized coal occurs within the furnace. Furthermore, it has been difficult to remarkably lower an amount of consumption of oil. Systems of this kind are disclosed, for example, in JP-Y2-62-34l27, JP-A-59-95310, JP-A-5974423, JP-A-59-24ll8, JP-A-57-104026 and so on.
Additionally, in recent years, start-up and suspension tend to frequently be carried out in boilers for the power plant thereby resulting in an increase in an amount of consumption of oil.
In equipment of the aforementioned type, it is impossible to directly ignite pulverized coal, because the pulverized coal fed at the start-up is low in concentration. Accordingly, it has been necessary to burn auxiliary fuel such as oil or the like to ignite the pulverized coal.
It is, therefore, an object of the invention to provide a pulverized coal firing method and an equipment therefor which can directly ignite pulverized coal without the use of auxiliary fuel.
In order to achieve the object, according to the invention, mixture gas of pulverized coal and combustion air is fed to a burner device when a pulverized coal concentration of the mixture gas reaches a level equal to or higher than a stable ignition concentration.
Since, according to the invention, it is possible to directly ignite the pulverized coal, the necessity of using auxiliary fuel such as oil or the like is dispensed with. Since the necessity of using oil higher in price than coal is dispensed with, it is possible to reduce the running cost of the equipment. In particular, when the invention is applied to boilers in which a middle load operation is carried out, extremely high effects are offered. In addition, if there is no necessity of using oil, an oil tank and oil feed lines employed in the prior art are dispensed with. This makes it possible also to reduce the initial cost such as the cost of equipment or the like.
Moreover, since the pulverized coal fed to burner sections is immediately combusted, the uncombusted pulverized coal is prevented from being accumulated within the furnace, so that a danger of explosion within the furnace is eliminated, making it possible to prevent an abnormal rise in pressure within the furnace.